Ability to whitelist/blacklist items within the "fix-stack" setting.

[ClickErrorxD]

It would be super nice to have the ability to whitelist and blacklist what items do and do not get "fixed" upon picking up stacked items or dropping stacked items.
When fix-stack is disabled, items with a max-stack of 1 will be added to inventories with a max-stack size of 64. If a player picks up 80 picks, he will get 64 + 16, instead of 80 different items. fix-stack: true

I reported this as a bug, but I'd rather it just have a whole configuration added. #546